Thank the polar vortex for a foggy June

Chicago Tribune photographer Chris Walker gives some tips on how to take a great photo in the fog.

Chicago Tribune photographer Chris Walker gives some tips on how to take a great photo in the fog.

Robert McCoppinTribune reporter

Driving home from downtown Chicago recently, Jason Erkes looked up and noticed something missing — the city. It had disappeared in the fog.

“I posted on Facebook, ‘Where is the skyline?’” he said. “You could not see a single building.”

As president of Chicago Sport & Social Club, where he organizes beach volleyball along the lake, Erkes has seen players repeatedly running for cover in recent weeks, drenched by sudden downpours.

“The weather has sucked with an exclamation point,” he said. “This has been the worst season we can remember.”

The pattern represents the last vestiges of the past wicked winter — but forecasters say that’s about to change. This weekend will see hot, sticky, summer-like weather, though it may rain some more.

If you must blame something, blame the polar vortex. While no single factor determines the weather, meteorologists say that the warming of the Pacific Ocean last winter pushed warmer temperatures into the Arctic air mass. Like squeezing a balloon, that pressure caused a bulge in the jet stream that sent bone-chilling air into the Midwest.

Even now, the jet stream is still with us, farther south than it normally would be at this time of the year, Accuweather meteorologist Mark Paquette said. That makes Chicago a battleground between warm air to the south and cooler drier air to north, causing rainstorms.

Statistics back up the complaints, showing this has been among the rainiest, gloomiest Junes on record. Fog has extended far enough to significantly reduce visibility at O’Hare International Airport seven days this month. The duration of fog and low cloud cover is quadruple normal levels, according to the National Weather Service.

The recurring mist is caused by warm, easterly winds blowing over a colder than usual Lake Michigan.

This past winter was the third-coldest and third-snowiest in Chicago’s record books, and it covered a record 93 percent of the lake with ice. Though water temperatures along the shore have reached the mid-60s, water in the middle of the lake was 40 degrees on Tuesday — the coldest it’s ever been this late in the year, meteorologist Gino Izzi said.

“That’s pretty incredible,” Izzi said. “I’d say the cold winter is likely playing a role in the weather of the past week or so.”

The fog is not only chilly — it can be dangerous. As U.S. Coast Guard responded to a mayday call on Lake Michigan fog recently when sailors could hear other boats cutting through the water near them — but couldn’t see them.

Heavy fog cut visibility to 75 yards on the water, Petty Office Second Class Brad Houston said. The Coast Guard spent five hours searching the waves, and every two minutes blasted its horn to warn other boaters away.

“The fog is an annoyance,” Houston said. “It makes things difficult.”

While Chicagoans know summer is always cooler by the lake, this year the effect has been especially pronounced. The average lakefront temperature downtown is slightly below normal, Izzi said, and on several recent days the difference between lakefront temperatures and west suburban Aurora has been 15 or more degrees — once as much as 21 degrees.

Tom Skilling, meteorologist for WGN-TV, said it’s also been very rainy, with more than seven inches falling at Midway Airport — more than twice the normal amount for June.

“We’re marrying an unusually cool lake with a very moist atmosphere,” he said.

Eventually though, he said, thermal inertia will take over. While June 21 marked the longest day of the year, he said, it typically takes one month to reach the hottest average air temperature, then another month for the lake to hit its peak temperature.

Some models and conventional wisdom suggest a cool summer following the cold winter this year. But Skilling notes that the official average temperature at O’Hare International Airport this June has been 70 — slightly above the normal of 68. So in the long run, he says, he expects a normal to warmer summer.

Chicagoans may soon be longing for a breath of that San Francisco chill.